Adds a new paragraph (3) to subsection (b) imposing an additional 1.2 percent hospital insurance tax on self-employment income above specified thresholds ($500,000 for joint returns; 1/2 of that amount for married filing separately; $400,000 for others). Also updates cross-references in subsection (b)(2)(B) (technical amendment from section 3121(b)(2) to 3101(b)(2)) and coordinates the new threshold amounts with wages taken into account for FICA taxes.

Replaces paragraph (1) of subsection (b) with new text that alters how net earnings from self-employment are computed and allocated when the Social Security contribution and benefit base is less than $400,000, specifying how excess earnings over the contribution and benefit base and amounts over $400,000 are treated in the computation.

Modifies the definition/exclusion of wages in paragraph (1) to limit the exclusion so that when the Social Security contribution and benefit base is less than $400,000, only remuneration exceeding the base but not exceeding $400,000 is excluded; adds a new subsection (aa) providing special rules treating predecessor-paid remuneration as paid by a successor employer for purposes of subsection (a)(1).

Adds a new paragraph (3) to subsection (b) imposing an additional 1.2 percent hospital insurance tax on wages above specified thresholds (different amounts for joint returns, married filing separately, and other filers), in addition to existing hospital insurance taxes.

Multiple amendments to section 1411 expanding the net investment income tax: adds a new subsection (f) that increases tax liability for high-income individuals by (i) substituting 'the greater of specified net income or net investment income' into the application of subsection (a)(1) for certain taxpayers, (ii) providing a phase-in limit, (iii) adding an additional rate bracket that increases tax by 13.6% of specified bases for taxpayers above defined high-income thresholds, and (iv) defines 'high income threshold amount' and 'specified net income'; modifies definitions and special rules in subsection (c), adds a new paragraph (7) on certain foreign-corporation earnings and requires regulations for post-2025 distributions.

Amends section 201(a) of the Social Security Act to allocate a portion of the revenues from the tax imposed by 26 U.S.C. 1411 to the Federal Old-Age and Survivors Trust Fund and makes a conforming amendment to the fourth sentence to refer to the newly added paragraph.

Amends section 201(b) of the Social Security Act to allocate a portion of revenues from the tax imposed by 26 U.S.C. 1411 to the Federal Disability Insurance Trust Fund.

Amends section 1817(a) of the Social Security Act (codified at 42 U.S.C. 1395i(a)) to allocate a portion of revenues from the tax imposed by 26 U.S.C. 1411 to the Federal Hospital Insurance Trust Fund.